1. Field of the Invention
The present invention relates to a direct current (DC) stabilization circuit for an organic electroluminescent display device (e.g., organic light emitting diode display device) and a power supply using the same, and more particularly, to a DC stabilization circuit for an organic electroluminescent display device and a power supply using the same in which noise included in DC voltage can be removed.
2. Description of the Related Art
Unlike a passive matrix organic electroluminescent display device, an active matrix organic electroluminescent display device is provided with a thin film transistor for each pixel. Further, a positive power supply voltage (ELVDD) and a negative power supply voltage (ELVSS) are applied to the pixel having the thin film transistor. In particular, the positive power supply voltage is connected to a driving transistor generating a driving current.
The driving current generated by the driving transistor depends on a voltage difference Vsg between a source and a gate of the driving transistor. In addition, the driving transistor is connected to the positive power supply voltage so that the voltage difference Vsg of the driving transistor is directly affected by the positive power supply voltage. Thus, in the case where the positive power supply voltage does not continuously maintain a predetermined level due to noise or the like, the driving current generated by the driving transistor varies irregularly even though the same data signal is applied to the driving transistor.
FIG. 1 is a block diagram of a conventional power supply.
Referring to FIG. 1, the power supply includes a regulator circuit 100 receiving a first power supply voltage applied from an input power supply, and a variable resistor 150 for adjusting an output level of a second power supply voltage output from the regulator circuit 100.
By controlling the variable resistor 150, the second power supply voltage output from the regulator circuit 100 is adjusted to a predetermined level. Further, the first power supply voltage is directly applied from an external power supply or applied via an adapter. The adapter converts the power received from the external source into a power supply voltage having a plurality of levels.
The second power supply voltage output from the regulator circuit 100 acts as the positive power supply voltage of the organic electroluminescent display device. The regulator circuit 100 may be a series regulator, a switching regulator, or the like.
While the series regulator has disadvantages of low power efficiency and high heat generation, the switching regulator has advantages of high power efficiency and low heat generation compared with the series regulator. However, the switching regulator causes a ripple in an output signal because of noise generated in a switching operation.
When the first power supply voltage applied to the regulator circuit 100 includes the noise, the output level of the regulator circuit 100 cannot maintain a stable DC value. That is, when the second power supply voltage including the ripple is output, the driving current for the organic electroluminescent display device, depending on the positive power supply voltage, has an unwanted value so that a gray scale corresponding to the applied data signal cannot be accurately displayed.